From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2001-04-24T03:41:23+09:00
Subject: [ruby-talk:14098] Re: RCR: getClassFromString method

In article <988034673.396094.26164.nullmailer@ev.netlab.zetabits.com>,
Yukihiro Matsumoto <matz@zetabits.com> wrote:
>Hi,
>
>In message "[ruby-talk:14040] RCR: getClassFromString method"
>    on 01/04/23, Phil Tomson <ptkwt@shell1.aracnet.com> writes:
>
>|It would be nice to have a function that returns a class type given a 
>|string that names that class.  I realize that this is doable already in at 
>|least a couple of different ways - you can use the each_object method in 
>|ObjectSpace to iterate through all of the classes till you find the one 
>|you need, or you can use const_get in Modules, (at least that's where I 
>|think it is), but none of those ways is intuitive and easy to figure out 
>|for newbies.
>
>You are right.  None of them is intuitive and easy to fugure out.  But
>think about this: Should this really be encouraged style of programming?

Well, perhaps it shouldn't be encouraged, I don't know.  I'm not 
necessarily an OO purist, I suppose.

I know that I use this feature in a certain case where I have a class 
hierarchy like:

class Tool
  #methods to handle generic stuff common to PC and UNIX
end 

class Tool_PC < Tool
  #methods do PC specific stuff
end

class Tool_UNIX < Tool
  #methods do UNIX related stuff
end

Let's say that early on in the script I figure out what platform I'm 
running on, say:
$PLATFORM = "PC"  ($PLATFORM is global so I can instantiate 
Tool_"$PLATFORM" objects anywhere later on in the script)

Then I can instantiate the correct class based on the value of PLATFORM

There are probably other ways to do this, but getting the Class from a 
String seems pretty straitforward in this case - and it is how I've 
implemented this.

So maybe it's not a good 'pure' thing to allow, but it does have its uses.

Phil